1. Field of the Invention
The present invention relates to a sheet reversing and discharging device constructed to convey each of a tab sheet and an ordinary sheet in a particular manner, and an image forming apparatus using the same.
2. Description of the Background Art
Today, a printer, copier or similar image forming apparatus operable in a tab sheet mode is available. In the tab sheet mode, a tab sheet is inserted between ordinary printing or copying cycles in order to divide consecutive jobs. In a copier, for example, a tab sheet is conveyed with its edge opposite to an edge where a tab is present at the head, so that the tab does not obstruct conveyance. On the other hand, when the tab sheet is used as a slip sheet, it is necessary to reverse the tab sheet being conveyed with the tab at the head before discharging the tab sheet to a tray.
Japanese Patent Laid-Open Publication No. 3-107454, for example, discloses a device for reversing and then conveying a tab sheet. The device includes a path selector positioned at a branch portion on a conveyance path arranged in an image forming apparatus. The path selector, which is angularly movable, switches a direction in which a sheet should be conveyed, thereby delivering the sheet to a desired path. More specifically, the path selector nips a sheet between it and a roller positioned on a reversal path and is biased to exert a conveying force on the sheet. After the conveyance of the sheet, the bias acting on the path selector moves the path selector and thereby reverses the sheet. The path selector therefore contributes not only to path switching but also to sheet conveyance.
While an improvement over the device described above has been proposed, it has some problems left unsolved, as will be described specifically later.
As for control, the timing for reversal should be delayed by the length of the tab sheet in the direction of conveyance, resulting in low productivity. Specifically, Japanese Patent Laid-Open Publication No. 2000-16663 addresses to a problem to arise when a tab sheet is reversed by using the output of a sensor response to the trailing edge of the tab sheet as a trigger. Specifically, when the tab moves away from the sensing range of the sensor, control for reversal is apt to occur before the tab fully removes away from above range. In light of this, the above document teaches that the tab sheet is reversed with a margin in timing corresponding to the length of the tab after the sensor has sensed the trailing edge of the tab sheet.
While the margin taught in the above Laid-Open Publication No. 2000-16663 implements reliable conveyance, it delays the timing for reversal by the length of the tab after the sensor has sensed the trailing edge of the tab, again resulting in low productivity. To maintain high productivity, there may be sensed both of the leading edge and trailing edge of the tab sheet so as to calculate an exact timing for reversal on the basis of a length between the two edges. However, this kind of scheme is not practicable without resorting to sophisticated control.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 8-133587, 11-43265, and 2001-19211.
It is an object of the present invention to provide a sheet reversing and discharging device capable of reliably conveying even a tab sheet and an image forming apparatus using the same.
It is another object of the present invention to provide a sheet reversing and discharging device capable of insuring high productivity even with a tab sheet and an image forming apparatus using the same.
It is yet another object of the present invention to provide a sheet reversing and discharging device capable of setting a timing for reversal with simple control.
It is a further object of the present invention to provide a sheet reversing and discharging method having the above advantages.
In accordance with the present invention, a method of reversing an incoming sheet and then discharging it uses a reversal path for receiving a sheet carrying an image on one side thereof and then reversing the sheet, delivering members for delivering the sheet to the reversal path, and conveying members arranged on the reversal path for reversing the sheet delivered by the delivering members and then conveying the sheet. If the sheet is a tab sheet, the tab sheet is reversed in accordance with a time when the leading edge of the tab sheet is sensed. On the other hand, if the sheet is not a tab sheet, the sheet is reversed in accordance with a time when the trailing edge of sheet is sensed.
Also, in accordance with the present invention, a device for reversing a sheet and then discharging it includes a reversal path for receiving a sheet carrying an image on one side thereof and then reversing it. Delivering members adjoin the inlet of the reversal path for delivering the sheet to the reversal path. Conveying members are implemented as a drive roller and a driven roller for selectively further pulling the sheet entered the reversal path into the reversal path or conveying the sheet out of the reversal path after receiving the sheet. A drive source drives the drive roller. A controller causes, if the sheet is a tab sheet, the drive source to continuously drive the drive roller in a send-in direction until the tab of the sheet moves away from the delivering members or causes, if the sheet is not a tab sheet, the drive source to drive the drive roller in a send-out direction both when the sheet is sent in and when the sheet is sent out.